Utilizing Nonpolar Organic Solvents for the Deposition of Metal-Halide Perovskite Films and the Realization of Organic Semiconductor/Perovskite Composite Photovoltaics

Having captivated the research community with simple fabrication processes and staggering device efficiencies, perovskite-based optoelectronics are already on the way to commercialization. However, one potential obstacle to this commercialization is the almost exclusive use of toxic, highly coordinating, high boiling point solvents to make perovskite precursor inks. Herein, we demonstrate that nonpolar organic solvents, such as toluene, can be combined with butylamine to form an effective solvent for alkylammonium-based perovskites. Beyond providing broader solvent choice, our finding opens the possibility of blending perovskite inks with a wide range of previously incompatible materials, such as organic molecules, polymers, nanocrystals, and structure-directing agents. As a demonstration, using this solvent, we blend the perovskite ink with 6,6-phenyl-C-61-butyric acid methyl ester and show improved perovskite crystallization and device efficiencies. This processing route may enable a myriad of new possibilities for tuning the active layers in efficient photovoltaics, light-emitting diodes, and other semiconductor devices.

1:1 molar ratio, such that a 1M solution was obtained. The vial was sonicated until a dark yellowgrey suspension was obtained. The dissolution of the precursors was carried out in a modified version of a previously published methodology. 1 Briefly, a solution of methylamine (MA) in ethanol (Sigma Aldrich, 33 wt%)was placed into an aerator which was kept in an ice bath. A carrier gas, N 2 , was then bubbled into the solution, thus degassing the solution of MA. The MA gas which was produced was then passed through a drying tube filled with a desiccant (Drierite and CaO), before it was bubbled directly into the toluene (Sigma Aldrich) which contained the perovskite precursors. The gas was bubbled into the dark grey dispersion for 5 minutes after which 500 µl of butylamine (Sigma Aldrich) was added to the dispersion. Upon addition of the butylamine, a clear, yellow solution was obtained, after which toluene was added to the solution such that the final molarity of the perovskite solution was 0.5M. PCBM was then added to the precursor solution in the desired quantity, and the solution was stirred at room temperature until the PCBM was completely dissolved.

Deposition of Perovskite Films:
The perovskite films were deposited onto the desired substrate by spin coating at 2000 rpm for 45 seconds in dry air, resulting in the crystallisation of a yellow film during spin coating. The films were then annealed at 100 ℃ for 60 min, after which it was allowed to naturally cool down to room temperature. When the substrate was completely cool, the films were held in methylamine vapour for 10 seconds, causing a bleaching of the perovskite films. 2 The films were then removed from the vapour and immediately placed on a hotplate after which they were annealed for a further 15 minutes at 150 ℃, resulting in the formation of a CH 3 NH 3 PbI 3 perovskite film.

Optical Characterisation:
Absorption spectra were recorded on a Cary 3000 Uv-Vis spectrophotometer. Time-resolved PL measurements were acquired using a time-correlated single photon counting (TCSPC) setup (FluoTime 300 PicoQuant GmbH). Film samples were photoexcited using a 505 nm laser head (LDH-P-C-510, PicoQuant GmbH) pulsed at a frequency of 500 kHz, and fluence of 0.187 nJ/cm 2 .
The PL was collected using a high-resolution monochromator and hybrid photomultiplier detector assembly (PMA Hybrid 40, PicoQuant GmbH).

Device Fabrication:
Planar heterojunction solar cells were fabricated utilising previously published methods. were then transferred to a hotplate and annealed at 400 °C for 45 min before being allowed to cool down to room temperature naturally. When the substrate was cool the perovskite film was deposited and annealed as described above. 5 nm of C60 were then thermally evaporated under high vacuum followed by 1.2 nm of bathocuproine. Finally, 120 nm thick silver electrodes were deposited under high vacuum (10 -6 ) in a thermal evaporator using a shadow mask.

Current-Voltage Characterisation:
Solar cell performance was measured using a class AAB ABET sun 2000 solar simulator that was calibrated to give simulated AM 1.5 sunlight at an irradiance of 100 mW/cm 2 . The irradiance was calibrated using an NREL-calibrated KG5-filtered silicon reference cell. Current-voltage curves were recorded using a sourcemeter (Keithley 2400, USA). All solar cells were masked with a metal